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Diseases on Cannabis Plants

Diseases on Marijuana Plants

In the course of growing marijuana plants, one of the most stressful issues to face is diseases. Unfortunately, marijuana can be prone to a few different diseases, which most often arise as a result of nutritional deficiencies and improper growing conditions. Knowing the possibilities and being prepared for them before they occur will help to keep your marijuana plants growing healthy and strong.

Diseases are Considered Worst-Case Scenarios

While growing marijuana is not overly complicated, it does have its challenges. Although pests can be problematic, they are generally less challenging to handle than advanced diseases. Once disease sets in, it can spread rapidly among marijuana plants, taking all your hard work with it.

Types of Diseases that plague Marijuana Plants

Learn the different types of diseases that can affect your marijuana plants and how to recognize them.

Fungal Infections

Fungal diseases often originate from an overly moist atmosphere. There are many types of fungi spores in the air, and these grow best in humid environments. When too much moisture is coupled with too little airflow, fungi growth is going to prevail.

Fungal infections are typically the easiest to spot, but that does not mean they are simple to get rid of in the long run. The sooner the problem is identified, the faster measures can be taken to eradicate the problem.

Fungi are silent and opportunistic killers. Although there are many measures you can take to avoid them, once they have taken over, they can become a formidable enemy. If you are not aware of the subtle signs, the fungi can take over quickly, and plant death occurs rapidly.

Bacterial Infections

Unfortunately, bacterial infections are more challenging to protect against because their causes can sometimes be unknown. A bacterial infection can be spread by humans, pets, insects, water, and air. Sometimes, a plant can be a carrier of bacteria and show no outward signs, making it virtually impossible to protect your other plants. Knowing the signs of bacterial and fungal diseases is essential, so you will be able to safeguard your harvest.

Common Marijuana Diseases and How They Affect Plants

No matter how much care you take in growing marijuana plants, there is going to come a time when disease sets in. The best treatment for any plant disease is prevention. Here, you can learn about the most common diseases that affect marijuana plants, so you will be armed with the information that is necessary for offering the highest level of protection.


If you are growing in a hydroponic system, algae are going to be one of the biggest threats. Unfortunately, cannabis and algae both need the same nutrient-rich environment, which is why marijuana plants are so commonly attacked.

Algae destroy marijuana plants because they grow on their root systems, preventing them from being able to intake water successfully. Without water, any plant is going to die. Because the algae live at the root level, it can often be difficult for growers to know their plants are infected until it is too late. If you notice any of the following, algae may be the problem.

  • Wilting.
  • Burned edges on leaves.
  • Brown roots.
  • Leaf yellowing.

If algae have entered your hydroponic system, a complete flush and cleaning are critical. Using a ratio of 1:10 of hydrogen peroxide will allow you to clean the algae and destroy it. Putting the hydrogen peroxide mixture in your plant’s water supply will help to deliver much-needed oxygen, allowing your plants to get rid of the algae. UV lights can be used in the filtration system to destroy algae before it enters the growing area.

Bud Rot

Bud rot, formally known as Botrytis, is a disease that can quickly destroy cannabis plants and leave growers baffled. Regrettably, this disease is one of the most damaging because it ruins every area of the plant, consuming it in its entirety.

This pathogenic fungus is one of the most common to plague marijuana plants. Often called gray mold, it will destroy your entire crop in days, so it is essential to know the signs. The first sign of Botrytis is a graying of any part of the plant. If you notice graying and dullness, you must act quickly.

If you realize your marijuana plants have Botrytis, cut off the diseased areas right away. You should even cut into the healthy growth about one to two centimeters to ensure all the diseased portions have been removed. Make sure to destroy the diseased plant clippings and disinfect your hands, scissors, and all work surfaces. Keep the infected plants quarantined until harvest to ensure they do not infect others. You should also work to increase the air circulation in the grow room to prevent bud rot from spreading.

For prevention, keep the temperatures around 70 or higher and make sure to monitor humidity levels carefully. It is also a wise idea to wear protective clothing before entering your grow room. Botrytis spores can cling to your clothing, leading to you inadvertently exposing plants to the disease.

Leaf Septoria

Leaf septoria, also known as yellow leaf spot, causes distinctive yellow spots to develop on the leaves of cannabis plants. Most indoor growers will not experience leaf septoria because it is a fungus that typically grows after plants have been exposed to both heat and rain.

The first sign of leaf septoria is yellow spots on the lower leaves of the cannabis plant. As time goes on, the yellow spots will begin to spread rapidly throughout the leaves. In the worst cases of leaf septoria, the entire leaf will turn a bright yellow, becoming extremely dry and beginning to crumble.

In most cases, leaf septoria will not kill the plant. It can significantly inhibit cannabis plant growth and eventual yield though. Thankfully, there are some steps you can take to save cannabis plants if they have become infected with leaf septoria.

First, you are going to want to remove the infected foliage and destroy it immediately. Make sure to disinfect your hands, the grow room, and any tools used. Ensure your grow room remains at the right humidity level and increase air circulation to combat too much moisture, which can increase leaf septoria’s proliferation.

If you only have a mild case of leaf septoria, the above measures may be all that is needed. If the case is severe, fungicides may be required to bring it under control. Copper-based fungicides will quickly destroy the fungus and prevent it from spreading. Although essential oils can be used as a more natural alternative to treatment, they should never come in contact with your buds, or they could destroy the aroma and flavor.

Powdery Mildew

Powdery mildew is a spore-based mildew that can infect both indoor and outdoor cannabis plants.  Because the spores can be carried by the wind, it is challenging to protect your cannabis plants from powdery mildew.

Unfortunately, the spores of powdery mildew can lie dormant for a long time, hiding in the soil until the conditions are just right for ideal growth. This type of mildew is most often seen in cramped grow rooms without enough air circulation.

Powdery mildew is highly recognizable because it produces a fine white powder over all areas of the marijuana plant’s foliage. Unfortunately, this mildew can destroy a cannabis plant in record time.

To get rid of this mildew, use an apple cider vinegar spray or a hydrogen peroxide ratio. This will break down the cellular walls and cause the rapid destruction of the mildew before it causes death to your plants.


Fusarium is a disease that attacks the root system of a cannabis plant, killing it from the inside out. Fusarium does not occur in plants grown in hydroponic systems because it requires a soil substrate.

Plants that are infected with fusarium will experience stem rot, yellowing and wilting of foliage and eventual death. Unfortunately, it is almost impossible to treat fusarium once it has affected a plant because the outward signs do not begin to occur until the root system has been destroyed.

Verticillium Wilt

Verticillium is very similar to fusarium in the way it affects cannabis plant growth. You will most likely see this disease develop in cannabis plants that have way too many nutrients in the soil due to overfeeding or a lack of proper drainage.

Like fusarium, it is almost impossible to treat verticillium wilt once it has taken over because catastrophic damage has already been done.

Bottom Line

It cannot be stressed enough that prevention is critical when it comes to combatting diseases in marijuana plants. A healthy humidity level, the right temperature, and air circulation are all key to keeping diseases at bay.

If you notice your plants are showing signs of disease, do not panic. Act quickly and effectively to remove the threat as soon as possible. Although some marijuana plant diseases are treatable, some destroy the plant before growers are even aware it is present. Making a concerted effort to protect your plants and monitor their health is wise when growing marijuana indoors or outdoors.


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